Anatomy of Flowering Plants

I. Answer the following in one or two lines (1 mark each)

1. What is plant anatomy?

Study of internal structure of plant is known as plant anatomy

2. Name the undifferentiated cells in the plant body.

Meristems

3. Define a tissue.

A group of cells having common origin and perform one function.

4. Which is the tissue that gives rise to permanent tissue?

Meristematic tissues give rise to permanent tissues.

5. What are permanent tissues?

They are the tissues, which have lost their ability to divide as they have attained their mature

form.

6. Name the meristems responsible for primary growth in plant body.

Apical meristems, intercallary meristems, axillary bud & intrafascicular cambium.

7. Name the types of meristems based on the position in the plant body.

Apical, intercalary & lateral meristems.

8. What are simple permanent tissues?

A simple tissue is the one which is homogenous, made of only one type of cells, having a common

origin & function.

9. Name the three simple permanent tissues.

Parenchyma, Collenchyma & Sclerenchyma.

10. What are complex tissues?

They are the tissues, which are composed of two or more types of cells but contribute to a

common function are called complex tissues.

11. Name the two types of chlorenchyma.

Pallisade & Spongy

12. Name the living mechanical tissue in plants.

Collenchyma

13. Name the dead tissue in plants.

Sclerenchyma & Xylem

14. Why are sclerenchymatous cells dead at maturity?

Sclerenchyma cells mainly provide mechanical support to plant body. To perform this function,

cell walls are highly lignified & the protoplasm is obliterated. Thus they become dead cells.

15. Name the two types of sclerenchymatous cells.

Sclereids & fibres.

16. What are xylary fibres?

Fibres associated with the xylem are xylary fibres.

17. What are sclereids?

Sclerenchyma cells that are almost isodiametric with extensive lignifications of cell walls.

18. Name the secondary cell wall material in sclerenchyma cells.

Lignin

19. Name the types of vascular tissues.

Xylem & Phloem

20. What are the components of xylem/phloem tissues?

Xylem components – xylem tracheids, trachea, xylem parenchyma & xylem fibres.

Phloem components – sieve tubes, companion cells, phloem parenchyma & phloem fibres.

21. Name the essential elements of xylem.

Trachea & tracheids

22. Name the only living component of the xylem.

Xylem parenchyma

23. Why tracheids & vessels are called tracheary elements?

Tracheids & vessels are called tracheary elements as they take part in conduction.

24. What is the function of xylem fibre?

To provide support.

25. What is a proto-xylem/meta-xylem?

Proto-xylem – first formed xylem in the primary plant body.

Meta-xylem – later formed xylem in the primary plant body.

26. Define endarch/exarch xylem.

Endarch – when protoxylem faces the centre of the plant i.e. pith is known as endarch xylem.

Exarch – when protoxylem faces the periphery of the plant.

27. What is the function of xylem parenchyma?

Helps in the lateral conduction of water.

28. What are sieve tubes/sieve plates/companion cells?

Sieve tubes – are long slender tube like structures in the phloem of angiosperms formed by end

to end arrangement of sieve tube members with their end walls called sieve plates.

Sieve plates – a perforated plate at the ends of the sieve tube members.

Companion cells – are those which are associated with the sieve tubes, controlling their activity.

29. Define the following types of vascular bundles – radial/conjoint collateral – closed/open.

Radial – xylem & phloem occur as separate bundles on different radii as in roots.

Conjoint, collateral open type – where each vascular bundle is made up of both xylem & phloem

lying on the same radii, phloem on only side and separated by cambium.

Conjoint, collateral closed type – where each vascular bundle is made up of both xylem &

phloem lying on the same radii, phloem on only side and without cambium.

30. What is meant by dorsiventral/isobilateral leaf.

Dicot leaf is known as dorsiventral leaf as it shows morphological, anatomical & functional

differentiation along dorsal and ventral regions.

Monocot leaf is known as isobilateral leaf as it shows morphological, anatomical & functional

similarities along dorsal and ventral regions.

31. What is a stomatal apparatus?

It is a pair of guard cells alongwith specialized surrounding subsidiary cells that form a turgor

operated complex for transpiration and gaseous exchange.

32. What are apical/intercalary/lateral meristems?

Apical meristems are those which occur in root & shoot tips, primary in nature and increase in

length.

Intercalary meristems are those present inbetween mature tissues and are primary in nature.

Lateral meristems are those which occur along the sides of the plant body and bring about an

increase in the girth (thickness) of the plant organ and are secondary in nature.

33. Define the following:

Lenticels – Aerating pores on a dicot stem showing secondary growth.

Secondary growth – Increase in girth of plant organ due to extra tissues added by activities of

vascular cambium & cork cambium.

Interfascicular cambium – Cambium got by dedifferentiation of parenchyma of medullaryrays

adjacent to intrafascicular cambium.

Intrafascicular cambium – Meristematic cells present between xylem & phloem.

Periderm – Phellogen, phellem & phelloderm are collectively known as periderm.

Phellogen – Secondary cortex formed by the cork-cambium.

Phelloderm – The living inner derivatives of phellogen constitute the secondary cortex or

phelloderm.

Medullary rays – Are strips of parenchyma cells present between vascular bundles of dicot

stems. They maintain a living link between the pith and the cortex.

Epidermal tissue system – Outer covering tissue system of plant body which is formed from the

outer layer derived from apical meristem consisting of epidermis, stomata & epidermal

appendages.

Ground tissue system - It includes all the tissues excepting the epidermis and the vascular

bundles & it is the largest or the most exhaustive system, which begins from the layer next to

epidermis and continues right up to the centre of the organs in cylindrical bodies. It is

heterogeneous in nature, consisting of diverse types of cell elements adapted to carry on

different functions. In the axis of higher plants the vascular bundles occupy a restricted position

inside the stele or central cylinder.

Vascular tissue system - The vascular tissue system consists of the complex tissues, xylem and

phloem, which constitute discrete conducting strands called vascular bundles. These are usually

primary in nature.

Polyarch vascular bundle – Many vascular bundles

Bulliform cells – Are large, bubble-shaped epidermal cells that occur in groups on the upper

surface of the leaves of many monocots. They are generally present near the mid vein. These

cells are large, empty and colourless.

Brachysclereids (Stone cells) - Short isodiametric sclereids with branched pits.

Macrosclereids (Rod cells) – Rod like elongated sclereids with branched pits.

Osteosclereids - Bone-shaped sclereids (rod-like with swollen ends)

Astrosclereids - Star-like branched sclereids

Filiform Sclereids – Elongated sclereids with occasional branches

Tracheids – Elongated or tube like cells, thick and lignified walls with tapering ends.

Vessel – Cylindrical tube-like structure made up of many cells called vessel members, which are

short & wide without any end walls. Each with lignified walls and a large central cavity

Palisade parenchyma – The upper layer of ground tissue in a leaf, consisting of elongated cells

beneath and perpendicular to the upper epidermis and constituting the primary area of

photosynthesis.

Spongy parenchyma – A layer of irregular chlorophyll-bearing cells interspersed with air

spaces that fills the interior part of a leaf below the palisade layer – called also spongy layer,

spongy tissue.

Vascular Cambium – A plant tissue located between the xylem and the phloem in the stems and

roots of vascular plants. It is a cylinder of unspecialized meristem cells that divide to form

secondary vascular tissues

Cork cambium – A lateral meristem responsible for secondary growth that replaces the

epidermis in roots and stems.

Spring wood – Secondary xylem formed in spring season

Autmn wood - Secondary xylem formed in autmn season

Heartwood – Central part of secondary xylem that is dark in colour and non-conducting.

Sapwood – Peripheral part of secondary xylem that is light in colour & helps in ascent of sap.

Annual ring – Spring wood & autmn wood produced in one season constitutes an annual ring.

Dendrochronology – Study of the age of a tree by counting annual rings.

II. Answer the following briefly (2 marks each).

1. Give an outline general classification of plant tissues.

Tissues

Permanent Meristematic

Complex Simple Based on origin Based on position

1. Xylem

2. Phloem

1. Parenchyma

2. Collenchyma

3. Sclerenchyma

1. Primary

2. Secondary

1. Apical

2. Intercalary

3. Terminal

2. Give the differences between –

Meristematic & permanent tissues

Sl. No. Meristematic Tissues Permanent tissues

1 Living tissues Living or dead on maturity

2 Remain in a continuous state of division Lose the power of cell division either temporarily

or permanently

3 Do not attain a definite form or size Attain a definite form & size

4 Are undifferentiated or dedifferentiated cells Are differentiated cells

5 Do not carry out any function other than cell

division

Specialised to carry out specific functions

Simple & complex tissues

Sl. No. Simple tissues Complex tissues

1 A simple tissue is homogenous in nature Complex tissue is heterogenous in nature

2 Made of only one type of cells, having a

common origin & function.

Made of more than one type of cells with common

origin and work together as a unit.

3 Perform wide range of functions Meant for conduction of water & food materials,

hence are known as vascular tissues or

conducting tissues.

4 The various simple tissues in plants are

parenchyma, collenchyma & sclerenchyma.

Xylem and phloem constitute the complex tissues

in plants

Parenchyma & collenchyma

Sl. No. Parenchyma Collenchyma

1 Cells are isodiametric, spherical or oval in

shape

Cells elongated, polygonal, spherical, oval or

rectangular in shape

2 Loosely arranged with intercellular spaces Generally closely arranged without intercellular

spaces

3 Simple living tissue Simple living mechanical tissue

4 Also occurs in xylem & phloem Not found in xylem & phloem

5 Found in roots & stems Generally absent in roots & monocot stem

Parenchyma & sclerenchyma

Sl. No. Parenchyma Sclerenchyma

1 Cells are isodiametric, spherical or oval in

shape

Cell wall is uniformly thickened with lignification

2 Loosely arranged with intercellular spaces Give rigidity to the plant organ where present

3 Simple living tissue Simple, mechanical tissue, dead on maturity

4 Also occurs in xylem & phloem Occur in xylem & phloem

5 Found in roots & stems Present in roots & monocots

Collenchyma & sclerenchyma

Sl. No. Collenchyma Sclerenchyma

1 Simple living mechanical tissue Simple, mechanical tissue, dead on maturity

2 Cell wall is unevenly thickened without

lignification

Cell wall is uniformly thickened with lignification

3 Cells contain cytoplasm, nucleus, cell

organelles & vacuoles

Cells are devoid of cytoplasm, nucleus, cell

organelles & vacuoles

4 Cell give elasticity to the plant body/organ

wherever present

Cells give rigidity to the plant/body organ

wherever present

5 Generally absent in roots & monocot stem Present in roots & stems

Monocot & Dicot root

Sl. No. Monocot Dicot

1 Presence of exodermis in old monocot roots Absent in dicot roots

2 Wide cortex in monocot roots Not so wide in dicot root

3 Endodermis & pericycle cells thickened in

monotcot roots

Not thickened

4 No. of vascular bundles more than eight Less than eight

5 Pith is wide Small or lacking

6 Secondary growth absent Secondary growth present

Dicot & Monocot stem

Sl. No. Monocot Dicot

1 Presence of sclerenchymatous hypodermis Presence of collenchymatous hypodermis

2 Ground tissue undifferentiated Ground tissue differentiated into cortex,

endodermis, pericycle & pith

3 Vascular bundles are scattered Arranged in a ring

4 Vascular bundles are closed Open

5 Each vascular bundle surrounded by

sclerenchymatous sheath

Sheath absent

Dicot & Monocot leaf

Sl. No. Dicot (dorsiventral) leaf Monocot (isobilateral) leaf

1 Upper surface is dark green compared to

lower surface

Both the surfaces are equally green

2 Guard cells are kidney bean shaped Guard cells are dumb-bell shaped

3 Bulliform cells are absent Bulliform cells are present on upper surface

4 Mesophyll differentiated into palisade &

spongy parenchyma

Mesophyll is undifferentiated

5 Bundle sheath cells are colourless Bundle sheath cells contain chloroplasts

6 Bundle sheath extensions are parenchymatous Bundle sheath extensions are sclerenchymatous

Lenticels & stomata

Sl. No. Lenticels Stomata

1 Found in old stem & roots Found in leaves & young stems

2 Occurs in the cork tissue Occur in the epidermis

3 Contains a number of complementary cells Stomata has two guard cells

4 Are permanently open pores Open and close in response to turgidity of

guards cells

Exarch & endarch xylem

Sl. No. Exarch xylem Endarch xylem

1 Protoxylem occurs towards the periphery Protoxylem lies towards the pith

2 Metaxylem lies towards the pith Metaxylem lies towards the periphery

3 Exarch condition is found in roots Endarch condition found in stem

4 Found in radial bundles Found in collateral bundles

Protoxylem & metaxylem

Sl. No. Protoxylem Metaxylem

1 The first formed xylem elements are called

protoxylem

The later formed primary xylem is called

metaxylem

2 Made up of smaller & narrower tracheary

elements

Tracheary elements are larger and wider having

scalariform, reticulate and pitted thickenings

3 After some time, protoxylem gets crushed Remains functional throughout the primary

organ

Intrafascicular cambium & interfascicular cambium

Sl. No. Intrafascicular cambium Interfascicular cambium

1 Occurs inside the vascular bundles between

xylem & phloem

Develops between two vascular bundles

2 Develops from procambium Develops from medullary rays through

dedifferentiation

3 Primary in origin Secondary in origin

Open vascular bundle & closed vascular bundle.

Sl. No. Open Vascular bundle Closed vascular bundle

1 Xylem & phloem are separated by fascicular

cambium

Xylem & phloem are not separated by fasicular

cambium

2 Xylem & phloem move away from each other

due to the formation of new vascular tissue

Xylem & phloem remain in contact with each

other throughout

3 Secondary growth occurs Secondary growth is absent

4 Found in gymnosperms & dicot stems Found in monocot stems & leaves of most seeded

plants.

3. What is aerenchyma & where is it located?

A spongy tissue with large air spaces found between the cells of the stems and leaves of aquatic

plants.

4. Name the cell wall material responsible for uneven thickness of collenchymatous cells.

Cell wall thickened in the corner due to deposition of cellulose, hemicelluloses and pectin.

5. Mention the different types of parenchyma.

Based on structure & function, there are different types of parenchyma viz. chlorenchyma,

aerenchyma, storage parenchyma, xylem parenchyma, phloem parenchyma & stellate

parenchyma.

III. Answer the following questions in few sentences (3 marks each).

1. Explain the structural details of parenchyma/collenchyma/sclerenchyma with diagram.

Parenchyma:

Forms major component within organs.

Cells are isodiametric (having similar diagrams in all planes)

Thin cell wall made of cellulose.

Cells may be spherical, oval, round, polygonal or elongated shape.

Cells are closely packed or have small intercellular space.

Collenchyma:

Found either in homogeneous layer or in patches.

Cell wall thickened in the corner due to deposition of cellulose, hemicelluloses and

pectin. Cells are oval, spherical or polygonal in shape

Often contain chloroplasts.

No intercellular spaces.

Sclerenchyma:

Consists of long, narrow cells

Cell wall is thick and lignified.

Cell wall with few or numerous pits.

Cells are usually dead and without protoplast.

Provides mechanical support to the organs.

Sclerenchymas are of two types on the basis of origin, form & structure viz. fibres & sclereid.

2. List the functions of parenchyma/collenchymas/sclerenchyma/xylem/phloem.

Parenchyma:

1) Helps in storage of food, water & air.

2) Carries on vital activities like respiration, photosynthesis & conduction.

3) Capable of meristematic activity & can give rise to secondary meristems.

4) Aerenchyma gives buoyancy to aquatic plants.

5) Parenchyma cells associated with xylem & phloem help in conduction of water & food

materials respectively.

6) Parenchyma cells can dedifferentiate, acquire the power of division to form secondary

meristem which produce secondary tissues.

Collenchyma:

1) Provides tensile support to the young stems & leaves during development, provides elasticity

to the plant organs, preventing tearing action of wind on dicot leaves.

2) Presence of chloroplasts helps it to carry out photosynthesis.

3) Collenchyma cells have active protoplasts capable of removing the extra wall thickenings

during dedifferentiation which happens during the formation of cork cambium in dicot stems

& in response to wound healing.

Sclerenchyma:

1) Fibres provide strength & rigidity to the various organs of plants & enable them to withstand

various strains caused by external agencies without any damage to the inner thin-walled

cells, hence they are purely mechanical in support.

2) Sclerenchyma fibres, in the form of sheaths provide protection to internal parts of plant

orghans.

3) Sclereids provide hardness & mechanical strength to the plant organ where they are present.

4) Sclereids provide toughness to the otherwise soft pul of fruits & provide efficient protection

to the seeds in the form of shells.

3. Draw a neat labeled diagram of dicot stomata/ monocot stomata.

Dicot Stomata:

Monocot Stomata:

IV. Answer the following questions (5 marks each).

1. Explain the importance of studying anatomy.

Gives information about the internal structure of plant.

Indicates simplicity or complexity of organs.

Homology & analogy can be known only through the study of internal structure

Helps in differentiating various groups of plants, like stem & leaves of dicots & monocots.

Provides information about adaptations to diverse environments.

Anatomical studies can tell about adulteration, identification in forensic science and quality

of wood.

2. Give the important characteristic features of meristematic tissues.

Small, rounded/polygonal cells with no intercellular spaces

Cell walls thin and elastic

Nucleus large with dense cytoplasm

Central vacuole absent but small vacuoles may occur

Respiration & biosynthetic activities high. Food flow is high but there is no storage of food.

Meristematic cells grow and undergo repeated divisions

3. With the help of neat labeled diagram explain the different types of meristem based on their

position.

Depending on their location, the meristems are of three types, viz., apical, intercalary & lateral.

Apical meristem:

◦ Occurs in the shoot and root tips.

◦ Primary meristem

◦ Increase the length of plant

Intercalary meristem :

◦ Present in-between mature tissues.

◦ Primary meristem

◦ Occurs in grasses and regenerate parts removed by grazing.

Lateral meristem:

◦ Occurs in the mature regions of roots and shoots.

◦ Also known as secondary meristem.

◦ Responsible for producing secondary tissues.

◦ Fascicular vascular cambium, interfascicular cambium and cork cambium are

example of lateral meristem.

4. What are permanent tissues? Give their detailed classification.

The newly formed cells become structurally and functionally specialised and lose the ability to

divide. Such cells are termed permanent tissues. Permanent tissues are classified into simple

and complex tissues. Permanent tissues having similar structure and function are called simple

tissues. The various simple tissues in plants are parenchyma, collenchyma & sclerenchyma.

Based on structure & function, there are different types of parenchyma viz. chlorenchyma,

aerenchyma, storage parenchyma, xylem parenchyma, phloem parenchyma & stellate

parenchyma. Sclerenchymas are of two types on the basis of origin, form & structure.

Permanent tissues having many different types of cells which perform a single function are

called complex tissues. Xylem and phloem constitute the complex tissues in plants. Xylem

consists of tracheids, vessels, xylem parenchyma & xylem fibres, whereas, phloem is made up of

sieve tubes, companion cells, phloem parenchyma & phloem fibres.

5. Explain the composition of water conducting tissue/xylem in the plant body with the help of neat

labeled diagram.

Xylem consists of tracheids, vessels, xylem parenchyma & xylem fibres.

Tracheids : Elongated or tube like cells.

Thick and lignified walls and tapering ends.

Cells are dead and without protoplasm.

Inner layers of cell walls have thickenings which vary in forms.

Arranged parallel to the long axis of the plant body.

Have an empty lumen through which the water passes without any obstruction.

Vessels: Is a cylindrical tube-like structure made up of many cells called vessel members, which

are short & wide without any end walls.

Each with lignified walls and a large central cavity.

Cells are devoid of protoplasm.

Vessel members are interconnected through perforations in their common walls.

Presences of vessels are the characteristics of the angiosperm

Xylem fibres :

Have highly thickened walls and obliterated central lumen.

Either septate or aseptate.

Xylem Parenchyma :

Cells are living and thin-walled.

Cell walls are made up of cellulose.

They stored food materials in the form of starch or fat.

Also store materials like tannins.

The radial conduction of water takes place by the ray parenchymatous cells.

A. Tracheids B. Vessels C. Xylem parenchyma D. Xylem fibres

6. Explain the structure & function of phloem with the help of a neat labeled diagram.

Phloem is composed of four elements:-

◦ Sieve tube elements.

◦ Companion cells.

◦ Phloem parenchyma.

◦ Phloem fibres. Sieve tube elements : Long tube like structure arranged longitudinally

Associated with companion cells.

End walls are perforated to form sieve plates & the perforations are called sieve pores

A mature sieve element possesses peripheral cytoplasm and a large vacuole but lacks

nucleus.

Cytoplasmic strands are continuous from one sieve element to the next through sieve

pores.

P-proteins are proteinaceous material seen in sieve tubes as tubules and act as damage

control.

The function of sieve elements controlled by nucleus of companion cells.

Companion cells : Specialized parenchymatous cells.

Closely associated with sieve tube elements.

Connected with sieve tube element by pit field.

Have dense cytoplasm & prominent nucleus.

Control the functioning of sieve tube elements.

Helps in maintaining pressure gradient in the sieve tubes.

Phloem parenchyma : Made up of elongated tapering cylindrical cells

Have dense cytoplasm and nucleus.

Cell wall made of cellulose and has pits. Plasmodesmatal connections exist between the

cells through the pits.

Store food materials and other substances like resins and latex and mucilages.

It is absent in monocotyledons.

Phloem fibres : Also known as bast fibres.

Made of sclerenchymatous cells.

Absent in primary phloem but present in secondary phloem.

Much elongated, unbranched and have pointed, needle like apices.

Cell wall is quite thick.

On maturity loose their protoplasm and become dead.

Phloem fibres of jute, flax and hemp are used commercially.

7. With the help of neat labeled diagram explain the – T.S. of dicot stem/root/ monocot

stem/root/V.S. of dicot/monocot leaf.

T.S. of dicot stem:

Outermost layer is epidermis.

Epidermis covered with thin layer of cuticle and has trichomes and few stomata.

The cells arranged in multiple layers in-between epidermis and pericycle constitute the

cortex.

Cortex has three sub-zones :

◦ Hypodermis: a few layers of collenchymatous cells below epidermis.

◦ Cortical layers: consists of rounded thin walled parenchymatous cells with

intercellular spaces.

◦ Endodermis: it is the innermost layer of cortex. Cells are rich in starch grains and

are referred to as starch sheath.

Pericycle : present on the inner side of the endodermis and above the phloem in the form of

semi-lunar patches of Sclerenchyma.

Medullary rays: a few layers of radially placed parenchymatous cells present in between

vascular bundles.

A large number of vascular bundles arranged in a ring.

Each vascular bundle is conjoint, open and endarch protoxylem.

The central portion of stem constitutes the pith.

T.S. of dicot root:

The outermost layer is epiblema.

Presence of unicellular root hairs in epiblema.

The cortex constitutes many layer thin-walled parenchyma cells with intercellular spaces.

The innermost layer of cortex is endodermis.

Endodermis consists of single layered barrel-shaped cells without intercellular spaces.

Presence of casparian strip in the endodermis.

Next to endodermis there is few layer parenchymatous cells form pericycle.

Initiation of lateral root and vascular cambium during secondary growth takes place from

the cells of pericycle.

The parenchymatous cells present in-between xylem and phloem is called conjuctive tissue.

The number of xylem and phloem bundle is three or four.

All the tissues on the inner side of endodermis such as pericycle, vascular bundles and pith

constitute the stele.

T.S. of monocot stem:

Outermost layer is epidermis.

Epidermis covered with thin layer of cuticle and has trichomes and few stomata.

Sclerenchymatous hypodermis.

Vascular bundles are scattered in the ground tissue.

Each vascular bundle is covered by bundle sheath cells.

Vascular bundles are conjoint and closed.

Peripheral vascular bundles are smaller than central one.

Phloem parenchyma is absent.

Water containing cavities are present within the vascular bundles.

V.S. of dicot leaf:

Vertical section of a Dorsiventral leaf shows three main parts:

Epidermis.

Mesophyll cells.

Vascular systems.

Epidermis covers both upper (adaxial) and lower (abaxial) surface of the leaf has a

conspicuous cuticle.

Upper epidermis is continuous whereas lower epidermis is discontinuous due to the presence

of stomata, such a condition is known as hypostomatic leaf.

Abaxial surface has more stomata than the adaxial epidermis.

Tissue between upper and lower epidermis called mesophyll.

Mesophyll cells are two types:

Palisade parenchyma

Spongy parenchyma Adaxially placed palisade parenchyma is made up of elongated cells arranged vertically,

parallel to each other.

Spongy parenchyma: oval or round and loosely arranged cells below the palisade

parenchyma.

Vascular bundles are seen in the midrib and veins.

Xylem is towards the upper epidermis & phloem towards lower. Cambium is absent.

The vascular bundles are surrounded by a layer of thick walled bundle sheath cells which

are parenchymatous.

Between the bundle sheath & the epidermal layers there is collenchymatous bundle sheath

extension.

V.S. of monocot leaf:

Vertical section of a isobilateral leaf shows three main parts:

Epidermis.

Mesophyll cells.

Vascular systems.

Epidermis covers both upper (adaxial) and lower (abaxial) surface of the leaf has a

conspicuous cuticle.

Stomata are equally distributed on upper and lower epidermis, such condition is known as

amphistomatic leaf.

Mesophyll cells are not differentiated into palisade and spongy.

Vascular bundle is surrounded parenchymatous bundle sheath & there is sclerenchymatous

extension on either side.

In grasses, certain adaxial epidermal cells along the veins modified themselves into large,

empty, colourless cells called bulliform cells.

Causes rolling of leaves to reduce transpiration during water stress.

8. What is a vascular bundle? Explain the different types of vascular bundles.

Xylem & Phloem constitute a vascular bundle.

Based on the arrangement of xylem & phloem in a vascular bundle there are three types viz.

Radial vascular bundle: xylem and phloem form separate bundles & are arranged

alternately on different radii eg. Roots of seed plants.

Conjoint vascular bundle: xylem and phloem are present together in the same bundle

situated on the same radius. They are of two types viz. –

Collateral – Xylem & phloem lie together on the same radius, wherein xylem

lies towards the inner side & phloem towards the outside. In dicot stem

between xylem & phloem cambium is present and is known as open type

whereas in monocot cambium is absent between xylem & phloem and is

known as closed type.

Bicollateral – In some plants like the members of Cucurbitaceae family xylem

is sandwiched between outer & inner cambium & ploem i.e. outer phloem,

outer cambium, xylem, inner cambium & inner phloem and are always open.

Concentric vascular bundle: Xylem is surrounded by phloem & is known as

amphicribal found in some of the ferns; or phloem is surrounded by xylem & is

known as amphivasal found in Dracaena & Yucca. Such type of vascular bundles are

known as concentric vascular bundle.

9. Briefly explain the process of secondary growth in dicot stem.

Apart from primary growth the dicot plant exhibit an increase in girth is called secondary

growth. The tissues involved in secondary growth are two lateral meristem viz., Vascular

cambium & Cork cambium. Cells of vascular cambium present between primary xylem and

primary phloem is the intrafascicular cambium. The cells of medullary rays, adjoining these

intrafascicular cambium become meristematic and form the interfascicular cambium.

Intrafascicular cambium and interfascicular cambium join to form complete cambium ring. The

cambial ring becomes active and begins to cut off new cells both toward inner side and outer

side. Cells produced toward pith mature into secondary xylem. Cells produced towards

periphery mature into secondary phloem. Secondary xylem forms a compact mass, retaining

primary xylem in the centre. At some places, the cambium forms a narrow band of parenchyma,

which passes through secondary xylem and phloem is said to be secondary medullary rays.

During spring & autumn season, cambium produces spring & autumn wood respectively,

together they constitute an annual ring. The secondary xylem can be differentiated into

heartwood & sapwood.

Cork cambium or phellogen usually develops in the cortex region. Phellogen is a couple of

layers in thick. Made of narrow, thin walled and nearly rectangular cells. Phellogen cut new

cells to both inner and outer side. The outer cells differentiated into cork or phellem. The inner

cells differentiated into secondary cortex or phelloderm. The cork is impervious to water due to

suberin deposition. Phellogen, phellem and phelloderm are collectively known as periderm. Bark

is a non-technical term that refers to all tissues exterior to the vascular cambium, there fore

including secondary phloem and periderm. At certain region the phellogen cuts off

parenchymatous cells instead of cork. These parenchymatous cells rupture the epidermis and

forms lens-shaped opening called lenticels. Lenticels permit the gaseous exchange between the

outer atmosphere and internal tissues of the stem.